The present invention relates to a ferromagnetic amorphous alloy for use as material for magnetic appliances such as magnetic head, transformer, magnetic shield and so forth and, more particularly, to a ferromagnetic alloy of metal-metal amorphous alloy system having a superior thermal stability, high saturation flux density and substantially zero magnetic striction, usable in place of conventional ferromagnetic alloy of metal-metalloid amorphous alloy system.
It is known that, in some kinds of metal or alloy, it is possible to obtain an amorphous structure in which orderly arrangement of atoms is lost so far as a long range of atom arrangement is concerned, by cooling the metal or alloy in a molten state at a high cooling rate of about 10.sup.6 .degree. C./s under a specific condition. In recent years, it has been made clear that, among the amorphous alloys produced in the above-explained method, some alloys exhibit superior characteristics which could never be attained by the conventional crystalline alloys, such as high strength, high ductility, and superior soft magnetic characteristics, i.e. high saturation flux density and high magnetic permeability. These alloys are of metal-metalloid amorphous alloy system. A typical example of such alloys is an alloy of Fe-Co-Si-B system. For instance, an alloy having a composition of Fe.sub.4.5 Co.sub.70.5 Si.sub.15 B.sub.10 and an alloy having a composition of Fe.sub.4.8 Co.sub.75.2 B.sub.20 exhibit saturation flux densities which are as high as 8 to 11 kG. Since in the composition in which the ratio of Co to Fe contents is maintained 94:6, the magnetic striction becomes substantially zero, alloys having such composition can be used as the material of magnetic head, with the advantage that the change of magnetic permeability in the head production process is small. These amorphous alloys, however, are thermally unstable and time dependence is apt to occur regarding the magnetic characteristics thereof, because they are in pseudo-equilibrium state. Such thermal unstability is caused particularly in the amorphous alloys having non-metallic content such as B, C, P and Si. Such thermal unstable characteristic is considered to be caused by the diffusion and segregation of the non-metallic elements. In addition, since the non-metallic elements have no magnetic moment, the amorphous alloy containing non-metallic elements exhibits saturation flux density lower than that of the amorphous alloy consisting of only magnetic metallic elements.
Thus, there has been a demand for improvement in the thermal stability and saturation flux density of the metal-metalloid amorphous alloy.
Japanese Patent Laid-open No. 29817/1979 can be picked up as a reference showing a prior art relevant to the invention of this application.